[WCM] Added information about the new date handling in the comparison constraints and Range

| Q             | A
| ------------- | ---
| Doc fix?      | no
| New docs?     | yes (symfony/symfony#11673)
| Applies to    | 2.6+
| Fixed tickets | -
I have a minor question regarding this phrase:

```
If you want to fix the timezone ...
```

Does `fix` always imply that something is broken? In that case, we could change it for something like this:

```
If you want to use a custom timezone ...
If you want to set a different timezone ...
If you want to configure the timezone explicitly
```

What I mean is that the server timezone isn't broken, it's just different from what we may need.